The present invention relates to electrical connectors, and particularly concerns a modular AC-power attachment cord customizable to a number of different national-standard wall sockets.
Electrical equipment such as minicomputers and personal computers obtain their primary electrical power from a standard wall outlet. It would be more accurate to say that their power is from one of a number of quasi-standard wall outlets, for the plethora of different plug styles in use throughout the world is striking. At the same time, rigid national electrical codes not only prescribe prong configurations, but also minute construction details of plugs, wires, mountings, fuses, and so on. Attempting to manufacture a small computer or other electrical appliance to be marketed worldwide is greatly complicated by this problem.
In the early days of electric-power distribution, when, as Ambrose Bierce remarked of electricity that "it is already proved that it will pull a street car better than a gas jet and give more light than a horse," the purchase of an electrical appliance entailed a trip to the hardware store for the right kind of plug to fit the local type of wall socket. H. Hubbell, U.S. Pat. No. 1,275,693, proposed to alleviate this problem with a plug having a threaded insert and a template which could capture a pair of prongs in different positions. This plug, of course, requires knowledge and assembly by the purchaser, and is prone to spontaneous disassembly with repeated use. This is typical of other art in this area, such as U.S. Pat. Nos. 2,989,719 and 3,382,475. U.S. Pat. Nos. 2,417,928 and 2,450,657 employ this basic concept for connecting the wires in a power cord in different ways, to accommodate different voltages. U.S. Pat. No. 3,996,546 is a more modern configuration, in which a single insert can be positioned in a plug body in two different ways for different voltages. Such plugs require some instructions to and assembly by the purchaser, and are prone to loosening and spontaneous disassembly with repeated use. They are not very safe. They provide little or no strain relief for a cord connected to them.
As an international lack of standardization superseded local lacks of standardization as the most significant problem, other solutions have been tried. Requiring the customer to obtain or install his own plug locally is not feasible. At the present time, the favored approach is to make up a number of different attachment cords, each having a different national plug molded on one end and a common socket (such as an IEC type) molded on the other end. The equipment has a fixedly mounted, recessed common receptacle which accepts the common socket. This solution leaves much to be desired. It allows the distinct possibility of having an electrically hot plug coming loose from the equipment, or being pulled out accidentally, and wandering about on the end of a wire to be grasped, become wet, etc. Such attachment cords can also be lost or replaced with lower-rated sets which are inadequate for the equipment, and thus dangerous. The cords cannot be tested for continuity and insulation strength ("hi-pot" tested) as a unit with its associated equipment.
The best solution is to hard-wire the equipment when it is manufactured with a power cord having a direct connection and mechanical strain relief in the equipment at one end, and having the correct national-standard plug molded onto the other end. This solution, however, is expensive and time-consuming to the point of impracticability in most situations. It can create dozens of sub-model designations for essentially the same product, with the attendant blizzard of paperwork and inventory problems.